In recent years, global-scale environmental issues including global warming or energy issues including the start of the depletion of energy resources, such as oil, which were once believed inexhaustible are being recognized worldwide.
Under these circumstances, wind power generation not emitting CO2 is attracting lots of attention as energy producing means for resolving both the environmental and energy issues. However, a wind power generation apparatus, even a large wind turbine regarded to have high efficiency, can only convert approximately 40% of the kinetic energy of the wind flowing inside the wind turbine into electric power. If the amount of this conversion is improved, the wind power generation will occupy a more important place in the environmental and energy issues.
However, most of conventional wind turbines have an impeller exposed in the atmosphere, and there are many wind turbines installed in the peripheries of airports, for example. In the periphery of such an airport, an aviation Doppler radar is installed to monitor the movements of airplanes; however, the rotation of the wind turbines is frequently misidentified as the approach or taking off of small airplanes. This is recognized as a serious problem in regional airports in Europe and America, where many wind turbines are used in particular. However, a clue about how to solve this problem has not been found in the conventional wind turbines.
As a problem similar to this, there is a problem of bird strikes. The more the demand for wind turbines rises and the more the number of wind turbines increases, the more the frequency of flying birds being sucked into the impellers. Collecting broken impellers leads to reduction in the operating rate of the wind power generation and lowers the amount of contribution of the wind power generation to power supply.
The output of the wind power generation is proportional to the cube of wind velocity. Hence, when a wind turbine is installed, a windy district is selected as a location, and efforts have been made to collect wind as much as possible, to increase the velocity of the wind and to increase the amount of power generation. Accordingly, attention has been paid to improvement in the wind collector on the inlet side of a wind power generation apparatus, the impeller, the diffuser, etc. of the apparatus, and measures have been taken to improve the energy conversion efficiency thereof as much as possible. All these are assumed to be an extension of conventional turbo machines and the measures have been taken accordingly. Hence, there was a limit as a matter of course.
Under these circumstances, the inventors of the present invention and other researchers challenged the above-mentioned common knowledge about the wind power generation apparatus (see Patent Document 1). More specifically, they reached a viewpoint that it is not required to be obsessed with the conventional thinking of a streamline shape and a steady flow, provided that high output power generation can be attained. Conventional fluid machines are based on a streamline shape and a steady flow that are easy to analyze, and it is no exaggeration to say that there is no turbo machine that uses a non-streamline shape (bluff body) and an unsteady flow. However, even the non-streamline shape and the unsteady flow can serve the intended purpose of the machine, provided that a stable flow can be accomplished, that the velocity of an internal flow can be increased so as to be higher than that of a conventional flow, and that the flow can be improved. The streamline shape and the non-streamline shape are herein defined. The streamline shape is a shape according to which a flow does not substantially separate from the surface within a range of Reynolds number Re used in a fluid machine, and the non-streamline shape is a shape other than the streamline shape and in which the separation occurs.
Hence, to accomplish this, the inventors of the present invention proposed a wind power generation apparatus disclosed in Patent Document 1. This wind power generation apparatus is provided with a cylindrical wind tunnel body and a power-generating wind turbine disposed in the vicinity of the wind inlet of the wind tunnel body and adopts a configuration in which outside the edge of the outflow port of the wind tunnel body, a flat flange perpendicular to the flow direction of wind is provided to generate strong vortices therebehind when the wind flowing outside the wind tunnel body collides therewith. The wind tunnel body is an expanding tube, so to speak, a tube simply expanding from the installation position of the impeller to the outflow port, and the flange has a width of 10 to 100% of the minimum inside diameter of the wind tunnel body.
Providing this kind of flange (a ring) against the flow to form vortices is beyond the common knowledge on the conventional fluid machines. The vortices formed behind the flange are formed as the so-called Karman vortices generated alternately around the inner and outer circumferences being concentric with the ring on the downstream of the ring; the vortices are generated alternately (unsteadily) at certain timings and reduce the pressure in the vicinity of the outflow port of the wind tunnel body, whereby the difference in pressure improves the velocity of the internal flow.
It should be said that this configuration of the wind power generation apparatus has created a new category (a type of fluid machine having a non-streamline shape) in wind power generation apparatuses or fluid machines in which the entire flow around the fluid machine is controlled by the vortices generated on the outflow side, whereby strong wind is pulled into the apparatus and allowed to flow along the inner wall surface thereof to the outflow port so that the velocity of the flow is increased efficiently. This flow having the increased velocity can generate higher output power than that obtained by the conventional apparatus.